9-(Pyrrolidinium-1-yl)-9-boranuidabicyclo[3.3.1]nonane

The title compound, C12H24BN, is an adduct formed from 9-borabicyclo[3.3.1]nonane (9-BBN) and pyrrolidine. It crystallizes in the the triclinic space group P with three molecules in the asymmetric unit.


Structure description
Hydroboration has been proved to be a powerful tool in organic chemistry (Brown, 1961). 9-Borabicyclo[3.3.1]nonane (9-BBN) has found extensive use among the various hydroborating reagents because of its unique properties, commercial availability, convenient preparation, and enormous synthetic applications (Dhillon, 2007). The present work describes the synthesis and crystal structure of an adduct formed from 9-borabicyclo[3.3.1]nonane and pyrrolidine.
The title compound crystallizes in the triclinic space group P1 with three molecules in the asymmetric unit (see Figs. 1-4). On first sight, all three molecules look very similar. The B-N bond lengths are 1.632 (2), 1.631 (2), and 1.641 (2) Å in molecules A, B, and C data reports respectively. The sum of the covalent radii for nitrogen (0.74 Å ) and boron (0.81 Å ) is 1.55 Å if one includes the Schomaker-Stevenson correction for partially ionic single covalent bonds (Pauling, 1962;Schomaker & Stevenson, 1941). The B-N bonds found in the title compound are longer, which might be explained with the adduct character of the compound under investigation, which formally consists of R 2 BH À -NHR 2 + . Indeed, the closely related N-(9-borabicyclo(3.3.1)nonyl)quinuclidine has a B-N bond length of 1.676 (3) Å .
The boron and nitrogen atoms are bound to one hydrogen atom each. These hydrogen atoms are in an antiperiplanar orientation in all three molecules.
The 9-BBN unit has a unique geometry imposed by the catenation of the atoms in the bicyclic heterocycles. Both sixmembered rings B1/C1-C5 and B1/C5-C8/C1 are in a chair conformation in all three molecules. Differences between the three crystallographic independent molecules become visible with a closer inspection of the five-membered N1/C9-C12 rings. The conformational analysis was performed with the PLATON software (Spek, 2009(Spek, , 2020. The five-membered ring in molecule A is an envelope on C10A and twisted on C9B-C10B in molecule B. Molecule C has disorder at the C11 atom of the ring with site-occupation factors of 0.723 (8)/ 0.277 (8). Therefore, two ring conformations result here. The ring N1C/C9C-C12C is twisted on C10C-C11C. The ring Diagram of molecule A showing the atom-labelling scheme. Atomic displacement parameters are drawn at the 50% probability level.

Figure 3
Diagram of molecule B showing the atom-labelling scheme. Atomic displacement parameters are drawn at the 50% probability level.

Figure 4
Diagram of molecule C showing the atom-labelling scheme. Atomic displacement parameters are drawn at the 50% probability level.

Figure 5
Overlay between the three crystallographic independent molecules obtained by fitting the 9-BBN units.

Figure 1
The asymmetric unit of the crystal structure in the unit cell.
Intermolecular interactions are dominated by closepacking. No specific hydrogen bonds can be identified.

Synthesis and crystallization
1.34 g 9-BBN (11 mmol, synthesized from BH 3 ÁSMe 2 and 1,5cyclooctadiene) were suspended in 5 ml of toluene (VWR Analapuran, dried with MBRAUN SPS 800) and 1.75 g pyrrolidine (25 mmol, Sigma-Aldrich, distilled from sodium) were added. A gas evolved and the 9-BBN dissolved in the solvent. After standing overnight all volatiles were removed in vacuo. After recrystallization from CHCl 3 1.15 g of white crystals were obtained, which were used for further analyses and crystal structure analysis.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1.
where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.32 e Å −3 Δρ min = −0.20 e Å −3 Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

data-2
IUCrData (2023). 8, x230332 Refinement. Hydrogen atoms bonded to C were positioned geometrically and allowed to ride on their parent atoms, with C-H = 0.99 Å for CH 2 and 1.0 Å for CH (C1 and C5). U iso (H) = xU eq (C), where x = 1.2 for CH 2 and CH. Hydrogen atoms at nitrogen and boron were localized from residual electron density maps. Hydrogen atoms at nitrogen were freely refined. Hydrogen atoms at boron were restrained at a B-H distance of 1.08 Å (DFIX restraint in SHELXL).